The diagnosis of pulmonary edema is frequently made from characteristic findings on the chest roentgenogram that suggest an increase in lung water. Optimal radiographic technique depends on a cooperative upright patient, which is not possible with most critically ill patients. These patients may also have multiple radiographic abnormalities that make interpretation of the chest roentgenogram difficult. The ability of portable chest roentgenograms to accurately identify the presence of excess lung water and monitor changes in lung water has not previously been evaluated in critically ill adults who are intubated and ventilated and in the supine position when the films are exposed. In 12 patients the pulmonary edema seen on portable chest roentgenograms was given a score (0 to 390 points), which was then compared with a determination of extravascular lung water using the thermal-dye indicator dilution technique. A linear correlation was observed (r = 0.51; p less than 0.05; n = 73). Evaluation of a change in radiographic score vs a change in lung water showed no linear correlation (r = 0.1; p greater than 0.05). While portable chest roentgenograms exposed under the conditions described were a useful technique for demonstrating pulmonary edema, they were not accurate in monitoring modest changes in lung water in critically ill patients.